HINTS ON MELTING

How to Obtain Clean, Smooth Ingots—Crucibles Must be Warmed—Placing the Ingredients—Use of Sal Ammoniac and Charcoal—Importance of Thorough Mixing—Casting the Ingot—Location of Melting Room— A "Kink" in Wire Coiling—Silver Melting.
I
T is just as easy to get a good, clean, smooth ingot of gold or silver as it is a bar that is full of holes, grooves or blisters. The poor "melts" are gotten by indifferent or careless workmen, who figure that the sub¬sequent rolling will smooth out everything. As a matter of fact, where the bar is uneven the thinner spots simply stretch, and after rolling to a certain thickness, your plate is full of seams, or cracks and holes, necessitating a cutting out of these portions for remelting. This, of course, is double work and a useless waste of crucibles and gas, to say nothing of the time. Then again the melter may not have a technical knowledge of the principles of melting and is simply following some formula furnished him, or that he has acquired, or he has drifted into the melting room by force of circumstances. To those manufacturers and melters who have met with varying results, the writer proposes to give some little "kinks."
All crucibles, whether sand or black lead, should be first warmed before putting in the metal for melting. The alloy should be put in first, then the copper, then silver, and lastly the gold. The reasons for this are, first, that the alloy and the copper melt first, and secondly, they are protected by the silver and gold from contact with the gases of the furnace, thus greatly eliminating oxides from being formed. Sal ammoniac and powdered charcoal are the agents used to neutralize the gases that form in the crucible, the charcoal acting as a coating cover and the sal ammoniac to purify the alloy while in a molten state. The official melter of the United States assay office at New York uses powdered sal ammoniac and a very fine powder of charcoal which he obtains from the collections on the beams of his melt¬ing room. The powdered sal ammoniac is probably bought fresh often, hence is as good as the lump form. For the average jeweler the lump is better, as the strength remains in longer, a little piece being broken off and pulverized as needed. For charcoal the powdered willow, purchased from leading drug stores, is as good as any. Berge, of New York (the crucible manufacturer), handles a charcoal powder which is very good, but under a good stiff flame blows out of the furnace to a great extent and is wasted. It is also a trifle more expensive than the willow charcoal.
The sal ammoniac should be mixed with the charcoal in about equal proportions and enough should be put on top of the gold to cover well before placing in the fur¬nace. Have flame just show through the cover, starting rather scant and increasing the force just as metal is melting. Add a little more of the sal ammoniac and charcoal. When the gold begins to sink to the bottom of the crucible, showing that the other metals are melted, it should be gently pressed down with an iron rod. Some¬times the gold, especially if it is in plate form, will stick for some time as a sort of roof before finally dropping of its own accord into the molten mass in the crucible. As soon as it is melted, which is ascertained by inserting an iron rod or poker, the mass is well stirred.
If a crucible cover, in addition to the furnace cover, is not used, it is well to add a little more of the sal ammoniac and charcoal, stirring just before pouring.
Right here the writer wishes to emphasize the necessity of thoroughly mixing the melts. The old-time melters swear by the rolling down of the stock and cutting up of same and remelting to get a perfect alloy. This method undoubtedly helps, but is slow, involving as it does a double melting. Stir the liquid mass well, two or three times, or even more, keeping it well covered with charcoal. First stir to the right, then rapidly to the left, and then pour rapidly into your plate or wire ingot. In case of 18-karat gold do not pour too hot; let the crucible commence to show a dull, almost blackish-red be¬fore pouring. The 14-karat alloys and lower should be poured as quickly as possible to prevent the base metals from oxidizing by contact with the air. Just before pouring some melters blow in a pinch of saltpetre, placed in the end of a long brass tube. This clears up the surface of the molten metal and perhaps helps a little in getting a cleaner ingot.
Within the last four or five years, and since the first edition was printed, there have come into use a number of green gold alloys in 14-karat and 10-karat, and as the principal alloy used is silver, the melt must be held as in pouring the 18-karat.
The ingot should be well warmed and just moistened with oil to prevent the gold from sticking. Avoid an excess of oil, as it will cause holes or fissures in your bar. In getting bars for wire the writer recommends the open wire ingot. The bar should be well hammered, with annealings frequently to prevent cracks. In 18-karat do not anneal until you have given the gold two or three very heavy drafts in rolls to close the grain. This applies also to all other soft alloys, whether wire or plate. In melting spring gold or hard alloys for snaps, pin tongues, etc., where the base metals added are of nearly the same weight, the ingot bar or plate must first be annealed and allowed to cool off slowly before rolling. Do not hammer any hard alloys, but in rolling force the drafts, do not "baby" the stock. This starts a good grain in the metal.
The farther away or the better protected the melting room is from drafts or windows, the better will be the general results. The adding of saltpetre is very hard on the crucibles and is hardly worth while in the long run.
An old pair of canvas gloves will be found handy in facilitating the handling of the furnace cover, ingots, etc.
In rolling wire it may be interesting to the beginner to know that a close, even coil is obtained for annealing, or for convenience in putting in gold box, by pulling the end of wire back over the top roll. When the wire has all passed through, an even coil of about the diameter of the roll is the result. It is surprising that a number of melters to-day who have been in the business for years have not gotten on to this little "stunt" and are still bending the long strip into a coil by hand, getting an uneven coil and risking burning or melting the projecting strands in the subsequent annealing.
Silver is melted and poured pretty much like 18-karat gold. The points to remember are, that it should not be poured any hotter than is necessary and that it should be well stirred with an iron poker. Borax or boracic acid crystals are used in place of sal ammoniac; keep extra well covered with charcoal, add a little more borax as soon as silver is melted. Poke or shove the borax under the charcoal with a long, narrow pair of tongs. The ingot should be just hot enough to permit of the finger touching it for a moment. In annealing after rolling, do not get too bright a red heat, as this will cause air blisters, condemning many a good bar that un¬til then had been all right.